This invention relates to radiant energy analyzers having chart recording means, and more particularly to an analyzer, such as a spectrophotometer, having a first plurality of preselectable wavelength scan speeds and a second plurality of preselectable chart expansion values.
In spectrophotometer systems a wavelength scanning device is utilized to transmit radiant energy of differing wavelengths through a sample to measure an optical characteristic of the sample (e.g. absorbance or transmittance), this characteristic then being recorded in graphical form on a chart recorder as a plot of optical characteristic (ordinate) vs. wavenumber or wavelength (abscissa). In such systems the wavelength scanning device is driven by a motor at one of a plurality of predetermined speeds. The abscissa of the chart paper is likewise controlled by a drive motor which may drive either the chart paper with respect to a marker or pen or vice versa, at one of a plurality of predetermined speeds to effect abscissa scale chart expansion. In this manner an operator may selectively expand the abscissa scale to provide greater clarity in regions of interest where the spectrum may be crowded or, alternatively, may reduce the abscissa scale for uncrowded regions of the spectrum. In operation of the spectrophotometer, precise registration and synchronization of the wavelength scanning device and the chart recorder is necessary so that the spectrum scanned is exactly reproduced by the recorder to provide a clear and accurate spectrum of the sample being analyzed.
To provide the greatest flexibility in an instrument of this type the operator should be given a wide selection of wavelength scanning speeds and a wide selection of abscissa scale chart expansions. Unfortunately, some of the selected combinations of scan speed and chart expansion may be limited by the capability of the drive motors or may be otherwise unusable by the system. A selected combination which exceeds the torque vs. speed capability of the chart motor, for example, could not be accurately executed by the motor, and the resulting graphical plot for such a selection would be erroneous. Moreover, the necessary synchronization and registration between the wavelength scanning device and the chart recorder would be destroyed by attempted execution of an invalid selection, requiring the operator to interrupt system operation to re-register the wavelength scanning device and the recorder.